In recent years, there has been widely employed the optical stereolithographic molding method of a liquid photo curable resin composition based on data put in three-dimensional CAD, since this method makes it possible to obtain a desired three-dimensional fabricated object at a high dimensional accuracy without preparing a die or the like (see, for example, Patent Documents 1 to 6).
A typical example of optical stereolithographic molding techniques (hereinafter optical stereolithographic molding will be sometimes called “stereolithography”) is a method comprising selectively irradiating the liquid surface of a liquid photo curable resin in a container with an ultraviolet laser under computer control so as to give a desired pattern, curing the resin selectively at a thickness, providing a liquid resin for a single layer on the thus cured layer, curing it by irradiating with an ultraviolet laser in the same manner, and repeating the buildup procedure for obtaining cured layers to thereby give a three-dimensionally object. This stereolithography is widely employed today, since an object in considerably complicated shape can be easily produced thereby within a relatively short period of time.
Resins or resin compositions to be used in the stereolithography should have various characteristics, for example, having a high cure sensitivity upon irradiation with an actinic radiation, a fabricated object having a favorable resolution and a high fabricating accuracy, having a low volume shrinkage after curing, a cured object having excellent mechanical properties, having a favorable self-adhesiveness, having favorable curing properties under oxygen atmosphere, having a low viscosity, being excellent in water resistance and moisture resistance, absorbing little water or moisture with the passage of time, being excellent in dimensional stability and so on.
As photo curable resin compositions for stereolithography, various photo curable resin compositions such as photo curable resin compositions containing a radical-polymerizable organic compound; photo curable resin compositions containing a cationic-polymerizable organic compound; and photo curable resin compositions containing both of a radical-polymerizable organic compound and a cationic-polymerizable organic compound have been proposed and used. Examples of the radical-polymerizable organic compound to be used in these cases include (meth)acrylate compounds, urethane (meth)acrylate compounds, polyester (meth)acrylate compounds, polyether (meth)acrylate compounds, epoxy (meth)acrylate compounds and so on, while examples of the cationic-polymerizable organic compound include various epoxy compounds, cyclic acetal compounds, thiirane compounds, vinyl ether compounds, lactones and so on.
It has been a practice to control various properties such as the fabricating speed and the fabricating accuracy in the stereolithography, and dimensional accuracy, mechanical properties, water resistance and moisture resistance of the object obtained by stereolithography, by appropriately selecting a polymerizable component constituting a photo curable resin composition or combining two or more specific polymerizable components.
For example, it is known that an object by stereolithography having a high dimensional stability can be obtained by using a photo curable resin composition containing a cationic-polymerizable epoxy compound. In a photo curable resin composition containing epoxy compounds, moreover, it is proposed to use a photo curable resin composition which contains a cationic-polymerizable organic compound such as an epoxy compound together with a radical-polymerizable organic compound such as a (meth)acrylate compound so as to relieve a lowering in the fabricating speed caused by the epoxy compound having a low reaction speed (see, for example, Patent Document 7).
Although objects by stereolithography, which are obtained by the existing techniques, are excellent in fabricating accuracy, dimensional accuracy, heat resistance, tensile strength, water resistance, chemical resistance and so on, they are still insufficient in impact resistance, etc. For example, although the above-described object obtained by using a photo curable resin composition containing a cationic-polymerizable organic compound such as an epoxy compound together with a radical-polymerizable organic compound such as a (meth)acrylate compound is excellent in dimensional stability and so on, it is easily destroyed because of having an insufficient impact resistance.
With the diffusion of the stereolithographic techniques, there have been produced fabricated objects having complicated shapes or structures. For example, various fabricated objects having thin parts and small-sized parts are produced. When a fabricated object has a poor impact resistance in such a case, the object frequently suffers from breakage at a thin part or a small-sized part in the course of the production or utilization thereof. In recent years, moreover, fabricated objects are produced not only as mere models (dummies) but also as products for practical use such as matrices, processing members and machine parts. In these cases, it is required that the fabricated object are excellent in impact resistance as well as tensile strength. However, objects by stereolithography in the background art are still unsatisfactory from the viewpoint of impact resistance.
There has been known a photo curable resin composition comprising organic polymer solid particles and/or inorganic solid particles having a particle diameter of from 3 to 70 μm (see Patent Document 8). An object by stereolithography, which is produced by using the photo curable resin composition described in this Patent Document 8, has a phase state wherein the organic polymer solid particles and/or inorganic solid particles having a particle diameter of 3 to 70 μm are dispersed in the photo cured resin. Since the organic polymer solid particles and/or inorganic solid particles having a particle diameter of 3 to 70 μm are dispersed in the photo cured resin phase, this object has a low volume shrinkage and a high dimensional stability. Moreover, it has favorable properties, for example, excellent mechanical properties such as tensile strength and flexural strength, compared with a three-dimensional molded object without the above-described solid particles. As the results of examinations by the present inventors, however, it is clarified that the object by stereolithography has an insufficient toughness (or durability) in the photo cured resin phase and there is still room for improvement in the impact resistance thereof.
Furthermore, attempts have been made to add a specific polyether having hydroxyl groups at both ends to a resin composition for stereolithography containing a cationic-polymerizable compound having epoxy group and an a radiation-sensitive cationic-polymerization initiator to thereby prevent curing failure of the composition caused by oxygen, decrease shrinkage upon curing and improve the dimensional stability, load deflection and tensile elongation thereof (see Patent Document 9). As the results of investigations by the present inventors, however, it is clarified that a high load deflection and a favorable tensile elongation are hardly compatible in an object by stereolithography, which is obtained from the resin composition for stereolithography as reported by this Patent Document 9 and, moreover, the object has an insufficient impact resistance.
(Patent Document 1) JP-A-56-144478
(Patent Document 2) JP-A-60-247515
(Patent Document 3) JP-A-62-35966
(Patent Document 4) JP-A-2-113925
(Patent Document 5) JP-A-2-153722
(Patent Document 6) JP-A-3-41126
(Patent Document 7) JP-B-7-103218
(Patent Document 8) JP-A-7-26060
(Patent Document 9) JP-A-2003-73457